In a single effect absorption refrigerating system utilizing warm water obtained by a solar heat collecting apparatus, only a single effect operation can be performed and it is not possible to perform a double effect operation even though a heat source of high temperature such as vapor is available.
On the other hand, in a double effect absorption refrigerating system, the procedure of switching a double effect operation to a single effect operation is very complicated and it is not possible to perform a single effect-double effect combined operation. Accordingly, when a low temperature heat source for a single effect operation is not sufficiently provided, such single effect operation has to be stopped and only a double effect operation by a high temperature heat source must be performed. Thus, the low temperature heat source being not utilized, only a high temperature heat source is used and it is therefore not possible to efficiently utilize energy.